1. Field of the Invention
The present invention relates to an optical disk apparatus, and a method, a program, and a medium for calculating the amount of lens shift, which are applied, for example, in a drive apparatus comprising an optical head for recording onto and reproducing from an optical disk.
2. Related Art of the Invention
With the spread of optical disks in recent years, much attention is focused on the technique of carrying out tracking control with detecting and correcting the amount of lens shift for the purpose of more stable recording onto and reproducing from an optical disk.
The configuration of a prior art optical disk apparatus is described below with reference to FIG. 9. FIG. 9 is a block diagram schematically showing an example of an optical disk apparatus which carries out tracking control with detecting and correcting the amount of lens shift as described above.
An optical head 901 is means of converging laser light from a laser diode 904 serving as an example of a light source by means of a converging lens 903 serving as an example of light converging means, and of irradiating with it an optical disk 915 which is driven to rotate. The optical head 901 is also means of detecting the reflected light from the optical disk 915 by means of a photodetector 905 and thereby outputting the information recorded on the optical disk 915 and a detection signal used for focus control and tracking control.
The optical head 901 comprises driving means 902 of moving the converging lens 903 in a disk radius direction (tracking direction) and in a direction (focusing direction) approaching or departing the disk surface. Further, the optical head 901 can be conveyed in a disk radius direction by a conveying means 912.
The operation of the prior art optical disk apparatus is described below with reference to FIG. 9.
A detection signal output from the optical head 901 is amplified and processed by an RF amplifier 906, thereby being provided as a focus error signal and a tracking error signal to a servo processor 909.
The servo processor 909 controls an FC/TR driver 916 on the basis of the focus error signal and the tracking error signal from the RF amplifier 906. The FC/TR driver 916 outputs a drive signal for driving the driving means 902 which supports the converging lens 903 in the optical head 901.
As such, focus control and tracking control are carried out so that focusing and tracking are achieved appropriately on the optical disk 915.
The detection of the amount of lens shift is carried out either (1) using the DC component and the low-frequency component of the tracking error signal or (2) by a sensor (TPS) which in not shown in the figure but may be provided for detecting the amount of movement in the tracking direction of the driving means 902.
A conveyance error signal is generated from the detected amount of lens shift, whereby a conveyance driver 911 is controlled so that the conveying means 912 is driven. Accordingly, the optical head 901 is conveyed in the disk radius direction.
As such, conveyance control is carried out so as to correct the lens shift caused by track jumping, off-centering of the optical disk, and the like.
Nevertheless, in the above-mentioned prior art method in which the amount of lens shift is detected using the DC component and the low-frequency component of the tracking error signal, the error is large and has caused a difficulty in accurate detection of the amount of lens shift.
Further, in the method in which a TPS is provided for detecting the amount of lens shift, an extra component cost occurs, and errors are caused by a variation and a temperature-dependent drift in the sensor components, and the like. This has similarly caused a difficulty in accurate detection of the amount of lens shift.